1. Field of the Invention
The present invention relates to an image display and, more particularly, to an image display, which is adopted specifically in a navigation system, using real image data corresponding to images such as satellite photographs or air photographs of the surface of the earth.
2. Description of the Relevant Art
FIG. 34 is a block diagram schematically showing the principal part of a navigation system in which a conventional image display is adopted. A speed sensor 2 for acquiring the distance in which a vehicle travels by computing the vehicle speed, and a gyro sensor 3 for acquiring the direction in which the vehicle is headed are connected to a microcomputer 10, which concludes the position of one's car (vehicle) based on the computed distance in which the vehicle has traveled and the direction in which the vehicle is heading (self-contained navigation).
A GPS receiver 4, which receives GPS signals from satellites through an antenna 5, is connected to the microcomputer 10, which concludes the position of one's car based on the received GPS signals (GPS navigation).
A DVD drive 6, which can capture electronic map data and the like from a DVD-ROM 7 (a storage device such as a CD-ROM is also allowed) in which electronic map data and the like are stored, is connected to the microcomputer 10, which displays a map picture wherein one's car position is precisely shown on a display panel 9b with matching the concluded car position with the electronic map data (conducting so-called map-matching). Here, the electronic map data can be also stored in a DVD-RAM which enables a map to be updated or in an HDD (hard disk).
Switch signals that are output from a joystick 8a or button switches 8b arranged on a remote control 8, or switch signals that are output from button switches 9a arranged on a monitor 9 are input to the microcomputer 10, wherein the processing corresponding to these switch signals is conducted. For example, when capturing information about a travel goal from these switches, the microcomputer 11 finds an optimum route from one's car position to the goal and displays the optimum route as a guidance route with a map picture on the display panel 9b. 
Accordingly, in the navigation system, a map picture is displayed on the display panel 9b, and a goal entered by a user, a guidance route to the goal, one's car position mark corresponding to the current position of one's car, a past driving trail of one's car and the like are overlaid for display on the map. The navigation system has an excellent function in that, by seeing this display panel 9b sequentially, the user can obtain course information and reach the goal in accordance with the course information.
However, in the navigation system in which the above-described conventional image display is adopted, since a map image to be displayed is prepared by using map data, it is difficult to know the current position of one's own vehicle through the map image, or to grasp the actual situation around the current position of one's own vehicle.
That is because it is difficult to express the vertical relation between multilevel crossing roads or the like using the map image, and because there are actually a large number of roads, buildings and the like which are not shown on the map image.
As one of methods for solving this problem, an invention has been disclosed, wherein the current position of one's own vehicle is displayed on an air photo image that is prepared from air photo data (Japanese Kokai No. 05-113343). As an advantage in using the air photo image, buildings and the like as landmarks become very noticeable, so that it becomes easier to know the current position of one's own vehicle, and it can also be made easier to grasp the actual situation around the current position of one's own vehicle.
However, a navigation system with which the user gets sufficiently satisfied could not be realized simply by displaying air photo pictures.
In addition, it is not true that in any case an air photo image that is prepared by using air photo data makes it easier to know the current position one's own vehicle and also makes it easier to grasp the situation around the current position of one's own vehicle, as compared with a map image that is prepared by using map data. There are cases where the map image makes it easier to know the current position of one's own vehicle rather than the air photo image.
For those reasons, it appears that as the next generation of navigation systems, those in which both air photo images and map images are used, neither systems in which only air photo images are used, nor conventional systems in which only map images are used, as a matter of course, will be mainstream. Therefore, the proper use of both real images such as air photo images and map images, which have different features from each other, will be important in the future.